Systems for growing concentrated populations of shellfish

ABSTRACT

A system is described for holding dense population of filterfeeding organisms, such as free, or &#39;&#39;&#39;&#39;cultchless&#39;&#39;&#39;&#39; oysters and hardshell clams in a configuration opposed to currents of nutrient-laden sea water. The system consists of means that both channel currents, or water flows developed by pumping, gravity flow, or tidal forces and hold the populations in opposition to these currents. A distributing flow of water is achieved throughout the populations contained in the system so that individual members of the population may filter at optimum rates, with waste products of their filtering activities being removed by the current. The system is capable of taking tiny hatchery-derived seed and growing them to commercial maturity in a series of stages designed to optimize handling and feeding requirements at the various stages. At the stages where the organisms are approaching commercial maturity and require a greater current flow and more nutrients, the system is capable of developing an increased level of efficiency in regard to the utilization of resources of current flow and nutrients. At its most efficient level, the system contemplates harvest of a phytoplankton resource of any estuarial area at optimum sustainable levels.

United States Patent [1 1 Wiegardt, Jr.

[ Aug. 26, 1975 SYSTEMS FOR GROWING CONCENTRATED POPULATIONS OFSHELLFISH John L. Wiegardt, Jr., Box 2, Nahcotta, Wash. 98637 [22]Filed: Sept. 17, 1973 [21] Appl. No.: 398,088

[76] Inventor;

[52] US. Cl 119/4; 119/4 [51] Int. Cl A01k 61/00 [58] Field of Searchll9/2, 4, 3

[56] References Cited UNITED STATES PATENTS 463,397 1 1/189! Walton, Sr.119/4 1,660,259 2/1928 Elsworth 119/4 3,028,837 4/1962 Tuttlc ll9/2 X3,192,899 7/1965 Luccy et al. 119/4 3,641,982 2/1972 Woodridgc et al.ll9/4 Primary Examiner-Hugh R. Chamblee Attorney, Agent, or Firm-Seed,Berry, Vernon & Baynham 57 ABSTRACT A system is described for holdingdense population of filter-feeding organisms, such as free, orcultchless oysters and hardshell clams in a configuration opposed tocurrents of nutrient-laden sea water. The system consists of means thatboth channel currents, or water flows developed by pumping, gravityflow, or tidal forces and hold the populations in opposition to thesecurrents. A distributing flow of water is achieved throughout thepopulations contained in the system so that individualmembers of thepopulation may filter at optimum rates, with waste products of theirfiltering activities being removed by the current.

The system is capable of taking tiny hatchery-derived seed and growingthem to commercial maturity in a series of stages designed to optimizehandling and feeding requirements at the various stages. At the stageswhere the organisms are approaching commercial maturity and require agreater current flow and more nutrients, the system is capable ofdeveloping an increased level of efficiency in regard to the utilizationof resources of current flow and nutrients. At its most efficient level,the system contemplates harvest of a phytoplankton resource of anyestuaria] area at optimum sustainable levels.

5 Claims. 8 Drawing Figures muczsms SHEET 2 U5 3 FIGO 3 FIGO PATENTEUmeesms SHEET 3 SYSTEMS FOR GROWING CONCENTRATED POPULATIONS OFSHELLFlSI-I BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to a system for the. artificial growing of densepopulations of hatchery-derived filter-feeding shellfish such as freeoysters and clams, with means provided for holding these populations incurrents of nutrient-laden water. These means involve a flume system forgrowing the seed from hatchery sizes to intermediate sizes, with aspecial case for growing hardshell clams toward maturity in a flume, orspillway system. As the seed grows toward maturity, their requirementsfor current and for nutrients increase. A system is developed to providethese requirements. In this latter system, a progression of structuresis utilized, beginning with a basic raft structure and adding channelingextensions to this primary structure. Each addition to the primarystructure is designed to increase the' efficiency of the system inutilizing a basic current and phytoplankton resource.

The system is designed to operate wherever there are currents andphytoplankton resources available. The system can be designed to beexpanded to the limits of these resources.

2. Prior Art Relating to the Disclosure Oysters, in their natural state,reproduce by spawning free swimming larvae that diffuse into the watermedium. After a time for development, usually several weeks in duration,the larvae attach to suitable materials, usually clean, hard objectssuch as rocks and oyster shells. The natural home of the oyster is thususually an oyster reef where oysters continually attach themselves tothe shells of their predecessors, or a rocky beach or ledge. In theseareas, the same currents that carry the oyster larvae carry the planktonto the attached oyster from which its food is derived.

The reproductive cycle of the oyster has been used to advantage by manby placing cultch materials shells, rocks, sticks, etc. on which theoyster larvae attach, and then cultivating the resulting seed. One ofthe earliest methods of this type cultivation was to plant the cultchwith seed attached on suitable bottom" areas of estuaries in populationsdense enough to permit efficient care and harvesting. Using this type ofculture seed must be both cheap and plentiful as losses in the growingpopulation are high due to the actions of predators and silting.Further, the bottom areas are not the natural home for the oyster andfeeding conditions are usually not as good as those in natural reefs androcks where tide flows and currents are swifter. In the areas whereoysters reproduce naturally, however, the success of the setting oftenresults in overcrowding in the oyster population, both in terms of spaceand food.

To overcome the problems generated both by natural and bottom cultureand to ensure better seed survival and oyster growth, more advancedtypes of cultures, utilizing various means to suspend the oyster off thebottom have been developed. These means include trays to hold theoysters, and include also stick or shells with seed attached. Whenshells are used they are generally spaced out on wires or ropes.

Recent developments in hatchery techniques have made possible theproduction of adequate supplies of oyster and clam seed for commercialoperation regardless of natural sets. One of the results of hatcherytechnology has been the development of cultchless" or free oyster seedwhere oyster seed is produced that is not attached to cultch. A methodand apparatus for growing free oyster seed is described in US. Pat.

No. 3,517,648, wherein water containing nutrients is pumped continuouslythrough the seed population carrying food to and detritus from the seed.

The major problem with the use of free seed has been to take it throughfrom the tiny hatchery-produced stage to a size and condition where ithas commercial value. Present hatchery technology limits the size towhich the seed can be grown feasibly because of the costs involved inthe production of feed for the seed.

The single oyster seed, while ideal from the standpoint of hatcheryproduction, is virtually helpless in the natural sea bed environment ofconventional bottom culture. Without its cultch as a platform and ananchor, the oyster falls easy victim to predator, to minor currents, andto siltation. Culture of the single oyster demands a nursery stage wherethe seed oyster can grow under protected conditions to a size where itcan survive in efficient numbers in nature. Because space requirementsfor seed populations increase with the growth of the individual membersof the population, economy demands that nursery techniques be devisedwhich can grow the population at a level of concentration above that ofa single layer. Unless such means can be found, the cost for providingspace for the expanding populations to usable sizes makes each nurseryoperations prohibitive for, at least, the species of oyster experimentedwith by the applicant, the Crassostrea gigas, or Pacific oyster.

SUMMARY OF THE INVENTION Phytoplankton stand at the base of the foodchain of the sea, in the same manner that plants are the basis for thesechains of life on land. Both plant and phytoplankton are converters ofthe primary energy of sunlight into forms that can be utilized by otherorganic systems. They accomplish this conversion by means ofphotosynthesis. Phytoplankton, inasmuch as they are dependent uponsunlight, tend to live in the regions of the sea where sunlightpenetrates, and are distributed through the water medium to the depth ofthis penetration.

The currents that move the sea-water medium are based upon the forces ofwind and tides, and upon the massive circulation of the global seas thatis engendered by the effects of the sun, moon and earths spin.Localcurrents in a water body may be developed by pumping systems. Thesecurrents continuously turn over the seas, bringing nutrients from itsdepths, mixing these nutrients with those carried in from the rivers tothe continents, stirring in oxygen and other life-support elements, etc.This continuous stirring and circulating, under the influence of thesuns light and warmth, pro vides the matrix for the continuousregeneration of the phytoplankton resource.

Currents that circulate the sea-water medium carry with them thephytoplankton populations suspended therein. The phytoplankton are movedby the same forces that generate currents.

In the system of this invention, the forces that produce currents in thesea-water are utilized by channeling them into flows that opposepopulations of filterfeeding organisms. This channeled current flowbecomes the basis for a distributing flow among the single members ofthe populations. in this flow that is so distributed the phytoplanktoncarried in suspension are utilized by the filtering organisms making upthe population.

The system of the invention thus utilizes the forces of currents tocreate a flow that presents food and lifesupport elements to theconcentrated populations of the system, thereby allowing the individualmembers of the populations to feed at optimum rates. The same flowflushes away wastes, removing them from the vicinity of the concentratedpopulations. In this system, the variables of: (1) current force; (2)phytoplankton and life-support elements; and (3) filter-feedingpopulations are assembled within a set of channeling structures. Thesechanneling structures perform the dual role of: l. holding thepopulations in opposition to the channeled flow; and (2) channeling theflow into a proper configuration so as to oppose the population.

The individual filter-feeding organism extracts its food andlife-support materials from the sea-water medium by forcing waterthrough its gill membranes where such material are caught on particlesof mucous formed by the organism. The means for forcing water throughthe membranes are its cilia which beat the water into motion. With eachbeat of the cilia an amount of water is put in motion and is immediatelyreplaced with an equal amount at the point of displacement. The beatingof the cilia sets up a continuous current that moves nutrient-ladenwaters toward the gill membranes. The current continues for as long asthe cilia beats. As the mucous particles entrap food and particulatematerial, a set of secondary cilia move the food and material toward themouth of the organism. There, the food is ingested and the particulatematerial, bound in mucous, is rejected. it is essential that theparticulate material, as well as the wastes of metabolic activities, beremoved from the vicinity of the organism. In nature, currents removethese materials. In the system described currents are developed toprovide the same function.

The different filter-feeding organisms carry out their function ofchanneling water into their filtering apparatus by various means. Theoyster develops its major channels by allowing its shell to gapeslightly, thereby exposing an extensive gill structure. The clam has adouble siphon in its neck, one for carrying water down the neck and ontoa gill structure held in its body, the other discharging the filteredwater. Because the invention deals with the extension of therelationship between current, channeling structures, and filteringmechanism it is important to note the operation of these factors at thelevel of the individual organism. The efficiencies claimed for oursystem are based upon the same principles employed by the organism inits structure and actions.

As the filter-feeding organism carries out its filtering activities, itgrows to maturity. As it grows, its ability to filter and itsrequirements for nutrients increase. lt appears that the filtering ratefor the oyster, regardless of its size or state of maturity, is in theratio of one part oyster meat to 10,000 parts of water of equaldisplacement volume per 24 hour day. The establishment of this ratio,which may vary with temperature and available nutrients, enablesprediction of the capacity for any given current flow to support apopulation utilizing the system of the invention.

In nature. populations of filter-feeding organisms tend to concentratein the areas where tidal currents cause the free-swimming larvae tocongregate and where there is a suitable bottom or clutch for the larvaeto attach. Thus, in nature, the organisms are accustomed to both crowdedconditions and to competition for the available food resources. Forthese reasons, they are ideally suited for adaptation to theconcentrated populations of the system of the invention.

In the attempt to devise nursery techniques for growing hatchery-derivedoyster and clam seed, a relationship was established betweenconcentrated populations of shellfish and currents of water. If thepopulation of filter-feeding organisms is held in opposition to achanneled current of water so as to fill the dimensions of the channel,a distributing flow will result so that a supply of nutrient-laden waterwill be carried to the individual members of the population. From thisdiscovery, it followed that a balance could be arrived at for any systembetween the distributing current force, the supply of nutrient materialscarried therein, and the filtering population positioned in oppositionto the flow. Such balancing allows the individual members of thepopulation to operate at maximum levels of efficiency in developingbodily structure and desirable shell configurations.

In applying this principle of opposition to the development of systemsbased upon it, it became increasingly apparent that the same factorsthat apply to a single container that develops the distributing flow asit channels water against an opposing population of organisms wouldapply to the systems of containers. Such container systems could balancecurrent forces against the opposition of populations, thereby developingthe distributing flow throughout the system. Further, in the same mannerthat a single container may fill the dimensions of a channel that bringsa current of water to the container, thereby making all of that currentavailable to a filtering population in the container, a set of multiplecontainers could also fill a channel to create a much larger scalesystem of opposition in which populations of organisms of approximatelyequal mass and density could be placed in opposition to very substantialcurrents. (see FIG. 9)

The invention, therefore, consists of means for channeling currents ofwater to bring these currents against populations of filter-feedingorganisms, thereby creating the distributing water flows. All of thechanneling means are aimed at one objective-to enable the individualfilter-feeding organisms of the population held in the system to utilizethe phytoplankton resource at optimum levels.

In the system, the harvest of the phytoplankton resource is accomplishedwhile the populations are held at optimum concentrations for thatharvest in places where handling and maintenance operations can be mostefficient and without interference with the basic production of thephytoplankton resource. This system is in marked contrast to holdingdense populations of filter-feeding organisms in areas where thephytoplankton is producedhere, the presence of too many organisms canhave the effect of holding down phytoplankton production.

These channeling means or structures of this invention must provide thedual function of holding the populations and of channeling the currents.The basic function of confining the population while developing the flowof water is accomplished by the use of screened containers which retainthe population while permitting the passage of nutrient-laden watertherethrough. The population is further confined between solid portionsof the container that also serve to channel the current flow. Theindividual container becomes a channeling structure through which thecurrent flows through the population contained therein having means forretaining the populations in the flow so created. Because thedistribution of filter-feeding organisms in these containers is alwaysinfluenced by gravity, this distribution will tend to occur horizontallyacross the surface of any container in which a population is placed. Theonly time when such distribution will not be horizontal is when theforce of the current tends to displace a portion of the population outof this plane. As a practical matter then, the easiest way to develop anopposing current flow through a dense population is to change thedirection of the current from its natural horizontal flow to anupwelling or downwelling direction through the width of the population.Such changes in the direction of the current may be readily accomplishedin all cases except where the changed flow must overcome the force ofgravity. In this instance the water must be mechanically moved toovercome the gravitational forces. Changing the direction of currentinto an off-horizontal configuration is utilized throughout the systemsdescribed with the exception of the screen-retained populations in aflume as noted above.

A series of containers may be installed so that, as a whole, theyintercept a larger amount of current than can be intercepted by theindividual container. This incremental effect may be illustrated byincorporating grandstand" or venetian blind column designs into a raftmade up of several rows of such columns. The raft is anchored to a pivotpoint in the tide flow so that it always faces into the direction oftide flow which is itself a current flowing in the natural channelformed between the sea-bed and the sea-surface. Opposition to thecurrent flow is thus developed as the raft is held against the currentby its anchor and the potential for the distributing flow is therebycreated. By the addition of a filter-feeding population in each of thecontainers, the potential so created is utilized.

The potential for the distributing flow may be enhanced by the additionof structural means to retain the current in its opposing configurationat the face of the population, keeping it from escaping in lateraldirections around the raft. Such structural means may include devicesthat extend the outer dimensions of the raft in such a way as to help toretain the current.

The outer dimensions of the basic raft structure may be extended forsome distance from the raft in the direction of the current flow. Inaddition, venturi-type extensions may be extended rearward from thisstructure. These extensions may also include those originating at thesides and the bottom of the opposing structure. The extensions serve tofunnel the current into the raft structure holding the series ofcontainers. Pressures are created across the face of the raft structurethat increase the potential for more even and efficient distribution ofthe current through the populations, and for a greater utilization ofthe resources of the current.

The raft structure plus extensions may be further modified so that allof an available current flow is directed through the structures and intoposition against the filtering populations, thereby making available forthe use of the filtering populations all of the potential energies ofthe current flow and phytoplankton resource.

The system, in its broadest sense thus comprises: 1) means fordeveloping a current of nutrient-laden water up to the limit of theresources available for producing that current for distribution throughdense populations of filter-feeding organisms (2) container meansholding a concentrated population of shellfish in opposition to the flowof nutrient-laden water having side walls parallel to the flow of thenutrient-laden water and a configuration enclosing the flow to maintainopposition to the water fiow by the organisms throughout the populationcontained therein so as to evenly distribute the nutrient-laden waterthrough the population, and (3) means to develop sufficient waterpressure to force the nutrient-laden water through the conentratedpopulations in the container. The channeled currents of the nutrientladen water that are distributed through the dense populations ofshellfish may be developed from a number of sources, including gravity,pumping, or tide flow, using, if desired, by-product water flows ofother systems such as cooling water from thermal or nuclear powerplants. Oysters and clams can be used as filtering agents with thesystem of this invention to clean up algae and plankton populations inwater passing through the system.

The objects of this invention include; (I developing for any given areaof seawater medium a system for growing quantities of edible shellfishup to the limits of the currents that circulate the seawater medium andthe phytoplankton resource carried in these currents; (2) providing asystem of shellfish culture that has a greater degree of control overboth the shellfish organism and its environment through the variousstages of the life cycle of the organism than can be achieved underpresent culture systems; (3) providing a system utilizing thecombination of the potential energies of circulating water containingthe plankton resource and concentrated populations of filter-feedingorganisms to filter such water flowing by them for the purpose ofconverting the plankton to food energy for man; (4) providing a systemfor growing concentrated populations of shellfish capable of harvestingplankton resources at optimum levels of efficiency; (5) providingsystems for growing concentrated populations of filterfeeding organismsutilizing induced current flow and capable of developing suitablecurrent flow to grow populations (with desirable shell configurations)both uniformly and in very high densities; (6) providing a fiume systemholding a series of trays having foraminous bottom walls on which thefree oyster or clam seed rests, water being forced upwardly through thepopulation in the trays or through the population confined betweenadjustable screens; (7) providing a raft structure holding a densepopulation of the free seed, the raft designed to be anchored in a areaof tide flow wherein nutrient-laden water flows in opposition to thepopulation contained in trays to feed them and to carry away thedetritus generated; (8) providing a raft structure including a series oftrays with foraminous top and bottom walls held in a framework placingthe leading edge of each tray in the series below the following edge ofthe tray above it; and where means are employed to increase the flowthrough the tray-held populations; (9) providing a system holding adense population of filter-feeding organisms positioned across an areaof an estuary to cause the tide flow alternately entering and leavingthe artificial or natural estuary area to be forced through the system;(l) providing a system holding a dense population of filter-feedingorganisms positioned across either the intake or discharge of thepumping systems so that all of the water entering or leaving the systemwill flow through the filtering population held in the system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of onemeans of artificially growing oyster and clam seed utilizing a flumehaving removable trays holding the seed, the trays positioned in thewater flow down the flume and designed to force the water upwardlythrough the bottom of the trays through a dense population offilter-feeding organisms resting therein;

FIG. 2 is a partial vertical crosssectional view through two of theabutting trays illustrating the water flow therethrough;

FIG. 2A is a vertical cross-sectional view illustrating an alternatetray design;

FIG. 3 is a vertical cross-sectional view of a culture system for anchorin an area of tide flow or in a fixed installation wherein the leadingedges of each of the trays in the series holding the filter-feedingorganisms are below the following edges of the preceding trays ingrandstand or stairstep fashion;

FIG. 4 is a cross-sectional view through the system along section line4-4 of FIG. 9;

FIGS. 5 and 6 are schematic representations of a system utilizing thesystem of FIGS. 3 and 4 to cause the tide flow of water entering andleaving the estuary area to flow through the system.

FIG. 7 is a perspective view of a system pivotally anchored in an areaof tide flow, the containers for the filter-feeding organisms stacked ina venetian blind manner;

FIG. 8 is a partial vertical cross-section of the containers of FIG. 7along section line 7-7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Both the individualfilter-feeding organisms, with their biological adaptability andphysiological characteristics, and the requirements of a population madeup of these individuals must be considered in the design of a massculture system. Thus, the container in such a system must be open to theflow of nutrient-laden water. It must also hold the dense population offilterfeeding organisms in a configuration which opposes the flow of thenutrient-laden water. Further, opposition to the flow of the water bythe population must be maintained through the dimensions of thecontainer that parallel the water flow. When the dense population offilter-feeding organisms is held in a container so that thenutrient-laden water flows through the population, a distributing ordiffusing flow may develop in any container configuration ranging fromvertical to horizontal. Because the force of gravity tends to distributethe surface of the population in a horizontal plane, however, thesimplest way to create opposing flow is to do so in a container whosedimensions rise in a vertical plane through the height of the populationheld in it. When the container is in a current flow where gravitationalpressures on the surface are not a factor, current flow may be deflectedfrom its natural horizontal course into container configurations fordevelopment of the required opposition.

Referring to FIG. 1 a flume system is illustrated in whichfilter-feeding organisms rest in a series of trays having foraminousbottom walls positioned in the path of water flow through the flume. Theflume includes a bottom wall 10 sloping downwardly from the point ofintroduction of the water with upended sidewalls 11 and endwalls 12. Theflume may be divided into sections at spaced intervals along the lengththereof by separators 13. At the end of each of the sections is a drain14. Within each of the sections are positioned a series of traysadjacent one another in which the filterfeeding organisms rest.

FIG. 2 shows one tray designed in more detail. Each of the trays 15include vertical sidewalls l6 and a foraminous bottom wall 17. At theforward end of each of the trays are legs 18 which space the bottom wallof the tray from the bottom Wall 10 of the flume. Near the rear of eachtray is a baffle 19 extending the full width of the tray. Preferably thebaffle is positioned just forward of the rear sidewall of the tray andhas a height less than the height of the sidewalls of the tray. Each ofthe trays may be provided with a handle 20 if desired.

An alternate tray design is illustrated by FIG. 2A. Each tray includesthree upended sidewalls 82 con nected to a foraminous bottom wall 81.The rear sidewall is also foraminous. Parallel legs 83 extend down thelength of the sidewalls of the tray. The legs 83 preferably slopedownwardly beginning at the front of the tray from about /2 inch to 1inch giving a reverse slope to the bottom wall 81, thereby allowingnutrientcontaining water to flow evenly to the population resting on theupper surface of the bottom wall 81. The trays may be provided with ahandle 84 for removal and insertion of the tray in the flume. The lowerportion 86 of the rear wall of the tray forms a support for the tray,extends the full width of the tray and is designed to act as awater-stop to force the water upwardly through the bottom wall of thetray. Preferably the rear wall portion 86 is sloped rearwardly at anangle approximately 45 to provide smooth flow of water through the tray.Longitudinally extending supports 87 secured to the bottom wall 81 andthe front and rear side walls may be provided to aid in supporting theforaminous bottom wall 81. These supports should have sloped uppersurfaces to prevent seed from resting on them.

When the trays are positioned in the path of water flow down the flumeas illustrated in FIG. 1, water entering through conduit 21 from anutrient-containing water supply 22 is directed into each of thesections where it flows beneath the first of the trays positionedtherein until baffle 19 or rear wall 86 is encountered. Referring toFIG. 2 the baffle forces the water upwardly through the screen bottomwall of the tray over the top of baffle 19, down through the bottom wallto the rear of the baffle and to the next abutting tray.

With the tray design of FIG. 2A the trays must be spaced from each othera few inches to allow water exiting through the rear wall of one tray toturn below the next adjacent tray. Oyster or clam seed 23 resting in adense population limited only by the height of trays and flume in eachof the trays is thus provided with a con tinuous supply ofnutrient-containing water. The water aids in carrying away the detritusgenerated by the seed. The number of trays which can be positioned insequence in each of the sectioned areas is dependent on the populationof seed in each of the trays, the rate of flow of the water through thetrays, the size of the trays and other variables. Rather than as shown,a separate water supply can be provided to the forward end of each ofthe sectioned areas containing trays instead of channeling the waterdown a side channel 24 as illustrated in FIG. 1, the water diverted tothe forward end of each of the series of trays.

The water after passing over and through the series of trays containingthe filter-feeding organisms drains through opening 14 in the bottomwall of the flume. The water supply may be taken from any appropriatesource containing proper nutrients for the filter-feeding organisms.

Oyster and clam seed grown in the trays as described grow uniformlythroughout the length and height of each tray. The upward flow of watercontaining nutrients through the dense population of seed suppliesnutrients to all the organisms in the trays uniformly and permitsoptimum growth of the population.

The flume system illustrated in FIG. 1 may be stacked one above theother in a relatively small area to enable artificial growing of greatnumbers of oyster or clam seed to an intermediate size. The tray systemis housed within a suitable enclosure to prevent direct sunlight on thefree seed. Rather than the flume system shown clam seed may be grown byconfining a population between retaining screens and positioning thescreens in the water flow down the flume.

The rates at which the filter-feeding organisms filter the nutrientsfrom the water appear to be a function of basic metabolism and thedisplacement of volume of the individual filter-feeder. Where a fixedrate of flow is maintained in the flume, the volume of filter-feedingorganisms that can be supported in the flow remains relatively constantregardless of the size of the individual members of the populations.Preliminary experimentation with the flume system illustrated by FIG. 1indicates that the ratio between the gallons of water required for agiven population gallonage is in the range of 10,000 gallons of water to1 gallon of filter-feeder meat per 24 hour day. Many variables affectthis ratio, especially the ratio between gallons of water and thecurrent and the pounds of plankton carried by them.

FIG. 3 illustrates a system for culture of filter-feeding organismsincludes a series of trays having front, rear and side walls and ascreened bottom wall fastened together such that the leading edge ofeach tray is below the following edge of the tray above it relative tothe direction of incoming current flow through the bottom wall to createan upwelling of nutrient-laden water through the trays. The direction ofthe current relative to the structure may be reversed, producing adownwelling, evenly-distributed flow through the trays as well. Such astairstep or grandstand system, illustrated in FIG. 3, or a venetianblind system, as FIG. 8, has a number of distinct advantages for cultureof filter feeding organisms. These advantages include:

I. Adaptability of this design to systems ranging from rafts to fixedsystems where the trays are positioned within a fixed set of channels;

2. A system where a separate nutrient-laden strata of water is deliverdto each tray;

3. A system where the common surface between trays becomes the waterdeflector for the preceeding tray in the series, thereby developing theopposing flow through the entire series of trays;

4. A system where water flows through each of the trays withoutdistortion of the major current entering and'leaving the system;

5. A system where the trays are self-cleaning of detritus because of theforced water flow therethrough;

6. A system which is inexpensive to construct and adapted to mechanizedhandling;

7. A system wherein each tray takes a uniform bite" out of a column ofwater flowing in either direction along an axis essentially parallel tothe water level;

8. A system where, in a fixed installation, alternate upwelling anddownwelling currents are created through alternate phases of the tidecycle;

9. A system where, in fixed installations as a part of the pumpingsystem, continuous, one-way flows are created at either intake ordischarge.

Referring to FIG. 3, a series of trays, each having sidewalls 100, afront wall 101, and a rear wall 102, are fastened together in stairstepor grandstand fashion. The front and rear walls of each tray may bedisposed at a negative angle of from 3545 from the horizontal relativeto the incoming tide flow, although they may be disposed up to rightangles to the horizontal. The trays may be fastened together by pins,plates overlapping the intersection of the trays or by a common sideboard 104 as illustrated by FIG. 3. The front wall 101 of the first trayof a series of trays and the rear wall 102 of the last tray of theseries are preferably extended as illustrated in FIG. 3 to providesurfaces and 106 to complete the baffling of the tray complex fordirecting water flow through the respective trays. The top wall or lidof the trays may be a single screen 107 fastened to the side boards I04and upper walls of each of the trays. The size of the trays and angle ofthe front and rear walls of the trays can be varied according tocircumstances encountered, considering such factors as tidal energy,population density, wind and weather conditions, etc. Exemplarydimensions of each tray are, for example, 7 feet long, 4 feet wide, and6 to 12 inches deep. Small trays of the type illustrated in FIG. 1 maybe inserted in the larger trays of the complex for easier handling andmaintenance.

A variation of the stair-step or grandstand designis illustrated inFIGS. 8, the venetian blind concept. The grandstand design utilizes ahorizontally descending column of trays with horizontal screen bottomsso that the populations of filter-feeding organisms may be heldrelatively level against the flow of the current. The Venetian blindconcept, on the other hand, utilizes a vertically descending column oftrays with the screens at angles to the horizontal. The individual traysinclude solid top walls 30, bottom walls 32 and side walls 34 withscreened front and rear walls 36 and 38 at angles to the horizontalholding the filter-feeding population 40 therein.

A series of such trays may be grouped together as illustrated in FIG. 7at the rear of a raft structure 42 anchored in an area of tide flow. Theraft structure 42 includes vertical frame supports 44 at each of fourcorners joined by horizontal cross braces 46. Flotation means 48 such aspolystyrene foam blocks are secured to the upper part of the raftstructure. The raft includes solid side walls 50 and 52 and a solidbottom wall 54 to channel the nutrient-laden seawater through banks oftrays of the design illustrated by FIGS. 7 and 8 or FIGS. 3 and 4 ormodifications thereof. The side walls preferably diverge outwardly fromthe banks of trays to essentially funnel the current flow through thepopulations of filter-feeding organisms held in the trays. Outwardlydiverging water deflectors 56 may be secured as illustrated by FIG. 7 todeflect water flow along the side walls of the raft outwardly and createa partial negative water pressure at the rear end of the tray complex toaid water flow through the tray complex and aid in positioning the raftin the tidal flow. The raft structure is anchored by suitable means,such as a cable 60 to means 58 at the bottom of the water body so thatit is free to pivot and orient itself essentially perpendicular to theflow. The depth of the raft structure and tray complex should besufficient to take advantage of the major surface currents of theparticular water body generated by the incoming and outgoing tides.

FIG. 6 illustrated use of a system constructed as a barrier to the entryof water to and from a natural or artificially created estuary, so thatthe tide flow must pass through the channeling structures and intoopposition against populations in the tray structures. This systemcombines the food producing efficiencies of the estuary with theutilization of the energy of tide flow through the tray system to createa practical, largescale means of mariculture. For the most efficientoperation, the tray complex, either of the design of FIG. 3 or FIG. 8 orother suitable design, is constructed where estuarial areas are presenton both sides of the complex or in an artificially created diked areawhere an inner pond is contained between low tide phases by the complex.This system may be also constructed at the intake or discharge of largescale pumping systems, where large one-directional current flows arecreated. When utilizing a system such as illustrated by FIG. 6, thesystem must be adjustable to the changing surface level of the tide.This may be done in two basic ways: (1) the column of trays with bottomand sides enclosed by fixed structures may be hinged at the bottom andheld at the surface by floats to adjust for the changing height of thetide, and (2) dropping a barrier from above the high tide level to alevel near mid-tide so that all of the waters of the higher tide stagesflows through the channel beneath the barrier. In this instance, thecolumns of trays start at the barrier and descend to the bottomdimension of the channel. Care must be taken to avoid creation ofdestructive currents during low tide intervals. One such means is toconstruct a bottom structure which can withstand the stresses of strongcurrents, much as the spillway systems of a dam. Another means is tohold the channel bottom far enough below the level of extreme low tideto avoid the creation of such stresses.

Referring to FIG. 6, the tray complex 108, consisting of a series oftrays disposed in side to side relation of the type illustrated in FIGS.3 or 8, or modifications thereof, is secured at its lower end to a solidbarrier 109 extending upwardly from the bottom of the estuary to a level110 just below the height of extreme low tide and at its upper end to anupper barrier 11] secured at its ends by suitable means to land adjacentthe estuary. The upper barrier descends from or near the level 112 ofhigh tide to a lower level 113 at or near an average tide level. The twobarriers 109 and 11] cause the flow of water from incoming and outgoingtides to be directed through the tray complex. A series of such traycomplexes within the channeling enclosure may be utilized to makemaximum use of the nutrients contained in the water, thereby optimizingthe harvest of the nutrient resource as illustrated. Such a complex isalso useful in large-scale pumping systems where filtering populationswill filter out the organic components of the intake water. An exampleof such pumping systems are the cooling systems for steam generatorsused in the production of electricity. In such large-scale pumpingsystems along coastlines, systems such as illustrated in FIGS. 6 and 7can be placed so as to enclose the intake to the pump and extend fromthere in the direction of the incoming current far enough to hold asmany lateral systems as desired. The water flowing into the intake ofthe pump through the filter-feeding organ isms would be filtered free ofthe organic materials contained therein before entering the pumpingsystem.

It is not the intent of this application to go into means for handlingthe dense populations of filter-feeding organisms grown in thesestructures and for maintaining the structures at the most efficientlevel. It is apparent, however, that the groupings of trays into columnsand rows makes it possible to handle the trays and the populations inmultiples. Further, the growth and development of fouling organisms makeit desirable to expose the elements of the system to the air wheneverpossible in order to destroy these undesirable elements. Under theseconsiderations, means for removing columns or rows of trays for handlingon shore and replacing these units with others already loaded can beaccomplished with cranes operating from shore or floating on the water,depending upon the size and location of the systems involved. Thepopulations in the trays are also amenable to handling by pumpingdevices that operate below the water.

Generally it has been found that oyster seed obtained directly from ahatchery operation (generally about 1/10 inch in diameter) can be grownto any size desired, first in a flume system as in FIG. 1 and thenmatured in a raft or fixed system, with the timing of its removal fromthe flume system depending upon the availablity of space in the furthersystem and upon the degree to which space in the flume is taken up bythe growing population. For example, under optimum temperature andnutrient conditions, the population of oysters doubles its spacerequirements every week, increasing in displacement volume by about Asthe seed grows from the sizes produced in the hatchery operation it isremoved from the trays and screened to size then kept separated whenreplaced into trays. Seed can be removed from the flume at A inch, inch,inch diameter or larger sizes. The further systems described can be usedto grow the seed to harvestable size, or to intermediate sizes fromwhich it can be transferred to other methods of culture.

The embodiments of the invention in which a particular property orprivilege is claimed are defined as follows:

l. A system for artificially growing concentrated populations ofshellfish, comprising:

a downwardly inclined, elongated flume having a bottom wall and upendedsidewalls,

means for introducing a controlled flow of nutrientcontaining water tothe head of the flume, the water flowing by gravity to the lower endthereof, and

a series of trays holding concentrated populations of shellfishpositioned within the flame in the flowing water stream and adjacent oneanother, each of the trays including 1. a foraminous bottom wall,upended sidewalls and front and rear walls, 2. legs extending downwardlyfrom the bottom wall spacing the bottom wall of each tray from thebottom wall of the flume, and 3. baffle means transverse to the flow ofwater within the flume to force the flowing stream of water up throughthe foraminous bottom wall of each of the trays to continually feed theconcentrated populations of shellfish resting thereon and remove thedetritus thereof. 2. The system of claim 1 wherein the baffle means aresecured ahead of the rear wall of the tray.

3. The system of claim 2 wherein the top edge of the baffle of each trayis located forward of the rear wall and has a height less than theheight of the side walls of the tray so that the water Welling upthrough the foraminous bottom of the tray strikes the rear wall of thetray and is forced downwardly through the foraminous bottom of theadjacent abutting tray wherein it strikes the baffle therein and isforced upwardly through the free oyster or clam seed resting therein.

4. The system of claim 1 wherein each of the trays is removable from theflume and includes a handle.

5. The system of claim 1 wherein the foraminous bottom wall of each ofthe trays is inclined downwardly from the front to the rear, a portionof the rear wall is foraminous, and the baffle means is an extension ofthe rear wall extending below the bottom wall.

=l l =I

1. A system for artificially growing concentrated populations ofshellfish, comprising: a downwardly inclined, elongated flume having abottom wall and upended sidewalls, means for introducing a controlledflow of nutrient-containing water to the head of the flume, the waterflowing by gravIty to the lower end thereof, and a series of traysholding concentrated populations of shellfish positioned within theflame in the flowing water stream and adjacent one another, each of thetrays including
 1. a foraminous bottom wall, upended sidewalls and frontand rear walls,
 2. legs extending downwardly from the bottom wallspacing the bottom wall of each tray from the bottom wall of the flume,and
 3. baffle means transverse to the flow of water within the flume toforce the flowing stream of water up through the foraminous bottom wallof each of the trays to continually feed the concentrated populations ofshellfish resting thereon and remove the detritus thereof.
 2. The systemof claim 1 wherein the baffle means are secured ahead of the rear wallof the tray.
 3. The system of claim 2 wherein the top edge of the baffleof each tray is located forward of the rear wall and has a height lessthan the height of the side walls of the tray so that the water wellingup through the foraminous bottom of the tray strikes the rear wall ofthe tray and is forced downwardly through the foraminous bottom of theadjacent abutting tray wherein it strikes the baffle therein and isforced upwardly through the free oyster or clam seed resting therein. 4.The system of claim 1 wherein each of the trays is removable from theflume and includes a handle.
 5. The system of claim 1 wherein theforaminous bottom wall of each of the trays is inclined downwardly fromthe front to the rear, a portion of the rear wall is foraminous, and thebaffle means is an extension of the rear wall extending below the bottomwall.